When a tubeless pneumatic tire is manufactured, an air-impermeable inner liner is attached to the inner wall surface of the tire. With this inner liner, the pressure of air filled in the tire is retained.
Heretofore, the inner liner has been generally made of a rubber material from the point of view that the rubber material has excellent adhesiveness to an adjacent layer.
Specifically, a layer to be adjacent to the inner liner is also generally made of a rubber material, while the adhesion between rubber materials is relatively good. For these reasons, the constituent material of the inner liner has also been formed of a rubber material. Among rubber materials, a butyl rubber has been frequently proposed and used as a material for the inner liner since the butyl rubber has excellent air impermeability.
However, the butyl rubber has a disadvantage in reducing the weight of a tire due to a large specific gravity.
In recent years, a method as follows has been proposed for the purpose of reducing the weight of a tire as much as possible by overcoming the disadvantage of the inner liner using a butyl rubber as described above. In the method, a thermoplastic resin composition in which a rubber component is combined with a thermoplastic resin is used as a material for the inner liner. (See Patent Document 1, for example)
However, in general, in the case of a member containing a resin component, the resin component sometimes reduces the adhesiveness of the member to another member made of rubber. For this reason, when a thermoplastic resin composition in which a rubber component is combined with a thermoplastic resin is used for the inner liner as the above-described proportion, the inner liner does not always adhere well to another rubber sheet which will be a layer adjacent thereto.
Accordingly, the following problem occurs in an actual process of manufacturing a pneumatic tire. Specifically, in the process, the inner liner and a rubber sheet whose end portions in the circumferential direction are overlapped and spliced with each other are laminated while being pressed with a stitch roller on a making drum. At this time, in a level difference portion formed in a portion where the splicing is performed, lamination and adhesion may not be perfectly performed along the shape of the level difference portion. As a result, an air pocket is likely to be generated in the level difference portion since the inner liner is detached and spaced from the rubber sheet.
The air pocket generated at the time of lamination and adhesion leads to the following problem. When an uncured tire is cured in the succeeding process in manufacturing a pneumatic tire, the air pocket expands due to thermal expansion. Then, when a vehicle runs with the tire having an expanded air pocket, the inner liner maybe torn at the portion of the expanded air pocket. That is, the durability of the tire is decreased.
For this reason, a pneumatic tire having an air pocket is not marketed as a tire product.    Patent Document 1: Japanese Patent Application Kokai Publication No. 2002-80644.